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(1) Be sure the radiator is mounted in such a way that any twisting of the chassis is not transferred into the radiator. With the Hall radiator there is a temptation to just use long bolts from the mounting tabs to the chassis mounting points. But, mounted like that, any twisting of the chassis shall twist the radiator. The Hall radiator should have intermediate mounting straps between the radiator and the chassis. All assembled with rubber grommets and spacers that allow things to rotate & twist in relation to each other.
(2) Use pre-mixed coolant and change it every 18 to 24 months.
If it still develops leaks, I'd agree the soldering job on the core is botched, I've seen radiators like that. Instead of patching the core over and over, replace it.
-G